This summer I went with three month old twins and their sister to a Swedish island for a week. It involved a great deal of preparation and packing and it needed a ratio of 5 adults to 3 three children to get everyone safely there and back again.
Tove Jansson's 'The Summer Book' captures the atmosphere of a similar island in the Archipelago Sea but there are no baby twins on that island, just one little girl and her grandmother.